NUCLEAR MAGNETIC RESONANCE STUDIES OF CONFIGURATION AND LIGAND CONFORMATION IN PARAMAGNETIC OCTAHEDRAL COMPLEXES OF NICKEL(II) VIII. Tridentate Ligands Containing Oxygen Donors

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Abstract
The proton magnetic resonance spectrum of the nickel complexes of iminodiethanol (ide), 2,2′-ethylether diamine (eeda), diethylenetriamine (dien), dipicolinic acid (dpa), and cis, cis, 1,3,5, cyclohexanetriamine (tach) are reported. Spectra are also reported for the mixed 1:1:1 Ni(II) complexes of the above ligands and dpa and mixed complexes of Ni(dien)(tach) and Ni(eeda)(tach). Ni(dien)(H2O)3 2+ is found to exist in solution as a mixture of facial and meridonal forms with isomerization between the two forms being fast on the NMR time scale and with the facial isomer being ∼ 1.17 Kcal/mole more stable at 300°K. Ni(eeda)(H2O)3 2+ is found to exist primarily as facially coordinated species, the facial isomer being more stable by at least 0.25 Kcal/mole at 300°K. ΔH for the facial meridional reaction is positive for Ni(eeda)2+ and almost zero for Ni(dien)2+. δ Λ conversion is rapid for all cases of facial coordination and slow for all cases of meridional coordination. δ Λ conversion of meridional isomers is slow because this requires inversion of the central coordinating atom of the ligand.